Why Your Compound Scorches: Seven Root Causes
A structured checklist for diagnosing premature crosslinking, ordered by how often each cause actually turns out to be the problem.
Scorch stops lines and scraps material. It is also highly diagnosable if you work through the causes in order of likelihood rather than changing the formulation first.
The seven causes, most likely first
- •Storage heat history — masterbatch stored warm, or held too long before the final mix. Very common in summer.
- •Curatives added too hot — sulphur and accelerator going in above roughly 110 °C, or on a warm mill.
- •Ingredient lot change — a new carbon black or accelerator source with different surface chemistry or activity.
- •Accelerator level raised without reformulating the activator package.
- •Mixer cooling reduced — fouled jackets, higher cooling water temperature, or a longer cycle than the one the compound was developed on.
- •Zinc oxide or stearic acid level increased, which accelerates cure.
- •Cross-contamination — residue of a fast compound in the mixer or on the mill.
How to confirm
Measure t5 on the suspect batch and on a retained good batch on the same day, at the same temperature. If the suspect batch is materially shorter, the cause is in the compound or its history, not in the moulding press. Then work backwards through storage records, lot numbers and mixing logs.
Prevention that actually works
Set a maximum dump temperature and enforce it, require masterbatch to cool before the final pass, and record lot numbers for every ingredient. Most scorch incidents are traceable to a documented change once the records exist. ## Need the documents or today's price? Send us the grade, quantity and destination port — we return a quotation with COA and MSDS attached. Email manager@fipolymer.com or use the inquiry form on this site.